The present invention relates to annunciator and similar systems.
An annunciator is an alarm or monitoring device employed to call the attention of an operator to a change of condition. For example, in a modern oil refinery or chemical plant the process may be monitored by a variety of instruments, for example, thermocouples and other testing transducers. These instruments are electrically connected to field transmitters which, by means of connecting wire, transmit their analog signals to the control location, for example, a main control room.
At the control location the wiring, called "field wiring," from the field transmitters is connected to field terminals, generally the terminals of a terminal block, usually by screw connections.
Each field wiring terminal may be arranged on one side of a switch closure and a second terminal arranged on the opposite side of the switch. The two terminals are electrically connected by the normally open or normally closed switch. The second terminal is then hand-wired to a terminal in a separate input terminal block, usually located in an adjacent rack. That input terminal block is connected to printed circuit boards containing the solid-state electronic logic of the annunciator system. The output of the annunciator logic is connected by wires to the visual display or buzzer or other type of warning device, and the warning devices are often located in a main control room.
The hand-writing of connecting wires from the field wiring to the terminal block for the annunciator logic is relatively time consuming and expensive. If such connecting wiring is to be later changed, because of changes in the system, it may require an additional expenditure of time and money to rewire, by hand, the various connections. In addition, as in any hand-wired system, a chance for error exists. To avoid such error and to provide for subsequent maintenance and system changes, it is generally required to write an extensive, and expensive, documentation of the hand-wired system.
In a typical system more than 100 field transmitters may be connected in a single annunciator system for the purpose of monitoring the transducers connected to the field transmitters and to provide alarms upon predetermined changes in the processes being monitored. The field wiring may be connected to terminals in a rack located below a control room. The racks may be connected to annunciator display panels which consist of separate lights in back of small lettered translucent panels.
An example of the system's operation is that upon an unwanted temperature drop in a vessel a light will flash in the control room lighting a small panel saying, "temperature drop No. 10 vessel."